Using resources Mark schemes

Q1.

(a) Air

2

Steel

1

(b)

Allow 1 mark for the correct meanings linked to context but incorrect way around

1

(c) Damp litmus paper turns white

1

(d) Iron(III)

1

[6]

Q2.

(a) 50

1

(b) 5%

1

(c) any two from:

• cost (9 carat is cheaper)

• pure gold is soft

or

24 carat gold is soft

or

9 carat gold is harder

allow 9 carat gold is stronger

allow gold is an alloy in 9 carat gold

• can change the colour

2

[4]

Q3.

(a) N2 + 3 H2 → 2 NH3

1

(b) catalyst

1

(c) as pressure increases percentage yield increases

1

(d) 32−23

both readings correct

1

= 9 (%)

1

[5]

Q4.

(a) filtration

or

by passing through filter beds to remove solids

1

sterilisation to kill microbes

allow chlorine / ozone allow ultraviolet light

1

(b) water needs more / different processes

1

because it contains any two from:

• more organic matter

• more microbes

• toxic chemicals or detergents

2

(c) (as part of glassware attached to bung)

salt solution in (conical) flask

allow suitable alternative equipment, eg boiling tube

1

(at end of delivery tube)

pure water in test tube which must not be sealed

allow suitable alternative equipment, eg, beaker, condenser

1

heat source (to heat container holding salt solution)

1

if no other mark obtained allow for 1 mark suitable equipment drawn as part of glassware attached to bung and at end of delivery tube

(d) determine boiling point

1

should be at a fixed temperature 100°C

allow should be 100°C

allow if impure will boil at a temperature over 100°C

1

(e) high energy requirement

1

[11]

Q5.

(a) 1 × 10−2 g

1

(b)

1

(test tube 1) 5.44 %

and

(test tube 2) 0.854 %

1

4.586

1

4.59

1

allow ecf answer correctly calculated to 3 significant figures

allow 4.59 with no working for 4 marks

allow 4.586 with no working for 3 marks

(c) Level 3 (5–6 marks):

Detailed and coherent conclusions based on the evidence together with an evaluation

are given in a response that is coherent and well-structured. A range of relevant points is made demonstrating a broad understanding of the key scientific ideas.

Level 2 (3–4 marks):

An attempt to relate relevant points and draw conclusions or to make an evaluation. The logic may be inconsistent at times but builds towards a coherent argument.

Level 1 (1–2 marks):

Simple descriptive statements are made. The logic may be unclear and any conclusions,

if present, may not be consistent with the reasoning.

0 marks:

No relevant content.

Indicative content

Simple statements

• nail rusted in test tubes 1 and 5

• test tubes 1 and 4 contained air / oxygen and water

• nail did not rust in test tubes 2, 3 and 4

• test tube 2 no water present

• test tube 3 no air / oxygen present

• test tube 4 paint stopped rusting

• test tube 6 scratched galvanised iron did not rust

• test tube 6 galvanising stopped rusting

Conclusions

• both water and oxygen are required for rusting

• coatings that prevent water and oxygen reaching the metal prevent rusting

• when paint is scratched, iron comes into contact with water and oxygen and the iron rusts

• in test tube 5 less iron exposed so less rusting than in test tube 1

• galvanising is better at resisting rusting than paint when scratched

• zinc is more reactive than iron, so when galvanised metal is scratched, zinc reacts with water and oxygen first / sacrificially

Evaluation

• oil and paint are effective at preventing rusting when the coating is intact

galvanising is the most effective coating because it prevents rusting even

when scratched.

6

(d) iron + oxygen + water

all three needed for 2 marks

2 correct = 1 mark

ignore air

2

[13]

Q6.

(a) all points correct

±1 small square

allow 1 mark for 6 or 7 plots

2

Year Percentage (%) of

bottles made from

other materials

1975 5

1980 10

1985 22

1990 42

1995 70

2000 72

2005 90

2010 95

1

(b) Level 3 (5–6 marks):

A detailed and coherent argument is provided which considers a range of issues and comes to a conclusion consistent with the reasoning.

Level 2 (3–4 marks):

An attempt to describe the advantages and disadvantages of the production and uses is made, which comes to a conclusion. The logic may be inconsistent at times but builds towards a coherent argument.

Level 1 (1–2 marks):

Simple statements made. The logic may be unclear and the conclusion, if present, may not be consistent with the reasoning.

0 marks:

No relevant content.

Indicative content

• glass – 2 stages in production of soda-lime glass

• glass – second stage, heating sand, limestone and sodium carbonate

• HDPE – 3 stages in production

• HDPE – second stage, cracking of naphtha to obtain ethene

• HDPE – third stage, polymerisation of ethene

• fewer stages in glass production, may be quicker

• higher temperature in glass manufacture, therefore maybe higher energy requirement

• glass bottle can be reused

• consideration of collection / cleaning costs to reuse glass bottles

• other glass products can be made from recycled glass

• plastic has greater range of sizes

• both produced from limited raw materials

• higher percentage recycled materials in glass conserves raw materials

This indicative content is not exhaustive, other creditworthy

responses should be awarded marks as appropriate.

6

[9]

Q7.

(a) ammonia and nitric acid

allow NH4OH

allow NH3(aq)

1

(b) shows fertilisers are formulations

allow gives percentage / proportion of nitrogen, phosphorus and potassium in the fertiliser

1

(so) farmers can choose fertiliser with required properties

1

(c) as world population increases, ammonia production increases

1

ammonia is used to produce fertilisers

1

so increasing need for fertilisers as more food required for increased population

allow as more food produced less mortality

1

[6]

Q8.

(a) because it is a good conductor of electricity.

1

(b) (i) 2.1 (%)

1

(ii) correct bar for calcium at 3.6 %

1

allow error of +/– 0.05%

correct bar for iron at 5.0 %

1

allow error of +/– 0.05%

(c) (i) decomposition

1

(ii) carbon dioxide

1

(iii) carbon = 1

allow one

1

oxygen = 3

allow three

1

(iv) 44 (g)

allow forty four

1

(d) (i) to make alloys for specific uses.

1

(ii) any three from:

• to conserve resources of iron or iron ore

allow steel instead of iron or iron ore

allow limited resource or non-renewable

• to avoid the need for quarrying/mining

• to conserve energy resources or fossil fuels

• to limit the amount of carbon dioxide produced or to reduce global warming

• to reduce the amount of landfill

“it” = steel

ignore cost and reuse and time and waste

3

[13]

Q9.

(a) (i) (thermal) decomposition

allow decomposes or endothermic

1

(ii) copper oxide

1

(b) (i) the (potassium) carbonate did not decompose/change/react (when heated)

allow temperature not high enough

do not allow potassium did not decompose

ignore references to reactivity

1

the mass did not change or the limewater did not go cloudy

1

because no carbon dioxide produced

1

(ii) the less reactive the metal the more (easily) its carbonate will decompose/react or vice versa

needs to be a relative comparison

2

allow max 1 mark where the distinction between a metal and its carbonate is not clear

allow 1 mark for carbonates of reactive metals do not decompose or vice versa

(c) (i) make it economical (to extract the metal/iron)

allow make it worth extracting

allow so they can make money/profit

1

(ii) Fe

1

balanced correctly (2,3,4,3)

not ecf

allow correct balanced equation but with 2Fe2 on right for one mark

1

(iii) iron from the blast furnace is brittle

1

steel produced is strong / flexible

allow steel has more/specific uses

allow steel is rust-resistant

1

“it” = iron

(iv) (recycling) is used to conserve iron (ore) or energy or resources or minimise pollution or reduce the need to quarry

allow reverse arguments.

1

(not reuse) because of damage, paint removal, rusting/corrosion, metal fatigue/weaker

1

(not landfill) because sites have limited space or loss of habitats

allow to reduce the use of landfill

1

[15]

Q10.

(a) (i) hard

ignore strong

1

(ii) hundred

1

(b) (i) Covalent

1

(ii) 3

1

(iii) Soft and slippery

1

(c) (i) cross-links

allow bonds

ignore links

do not accept intermolecular

1

(ii) melt

1

(iii) any two from:

• temperature

allow heat(ing)

• pressure

• catalyst

2

(d) (i) CH4

1

(ii) Small molecules

1

[11]

Q11.

(a) endothermic

1

(b) 82 (%)

correct answer with working gains 3 marks

if 17 or 34 not shown in working max 2 marks

accept 82.4

accept 82.35 to full calculator display (82.35294...) correctly rounded to at least 2 sf

if no answer or incorrect answer, then

(Mr =) 17 gains 1 mark or

14/17 gains 2 marks

OR

(2Mr =) 34 gains 1 mark or

28/34 gains 2 marks

OR

14/their Mr shown gains 1 mark or

correct calculation of 14/their Mr gains 2 marks

3

(c) (i) 7 / seven

1

(ii) H+ + OH– → H2O

1

(iii) ammonium chloride

allow NH4Cl

1

ignore an incorrect formula

(d) Marks awarded for this answer will be determined by the Quality of Written Communication (QWC) as well as the standard of the scientific response. Examiners should also apply a ‘best-fit’ approach to the marking.

Level 3 (5 – 6 marks):

Suggestion with reasons from all three graphs, and linking of ideas which may explain a compromise.

Level 2 (3 – 4 marks):

Suggestion with reasons referring to more than one graph.

Level 1 (1 – 2 marks):

Suggestion with a reference to a graph.

0 marks:

No relevant content.

Examples of chemistry points made in response:

A reasonable suggested amount of fertiliser would be in the region of 200 kg (per ha).

Accept any suggestion from about 180 kg (per ha) to 500 kg (per ha).

Yield:

• Using fertiliser improves yield.

• Yield improved most up to about 200 kg (per ha) of fertiliser.

• Yield only increased slightly above about 200 kg (per ha).

Profit:

• About 200 kg of fertiliser gives the most profit.

• Above about 200 kg (per ha) of fertiliser profit declines.

Run off:

• Run off is at low levels until about 300 kg (per ha) of fertiliser.

• Above about 300 kg (per ha) of fertiliser, run off increases.

Examples of linking of ideas:

• Overall 200 kg gives high crop yield and most profit.

• In conclusion 200 kg gives high crop yield and low run off.

• 200 kg gives most profit and low run off.

Examples of compromise:

• Profits go down after about 200 kg (per ha) of fertiliser because cost of fertiliser is not covered by increased yield.

• 200 kg gives the highest profit although it is not the highest yield.

• 500 kg gives the best yield but has the most runoff.

6

[13]

Q12.

(a) has delocalised electrons

accept free (moving) electrons

1

(so electrons) can move through the structure/metal

accept (so electrons) can carry charge through the structure/metal

accept (so electrons) can form a current

1

reference to incorrect particles or incorrect bonding or incorrect structure = max 1

(b) giant structure

accept lattice

accept each atom forms four bonds (with other carbon atoms)

ignore macromolecular

1

strong bonds

accept covalent

do not accept ionic

1

reference to intermolecular forces/bonds or incorrect particles = max 1

(c) thermosetting polymers do not melt (when heated)

accept thermosetting polymers do not change shape (when heated)

accept thermosetting polymers have high(er) melting points

ignore thermosetting polymers do not soften (when heated)

1

due to cross-links (between chains)

accept due to bonds between chains

1

reference to smart polymers = max 1

accept converse argument

[6]

Q13.

(a) (i) nitrogen: air

1

hydrogen: natural gas

1

(ii) as a catalyst

1

so the reaction speeds up

allow lowers activation energy or so a lower temperature can be used

1

(iii) cooled

1

ammonia condenses / liquefies

allow nitrogen and hydrogen remain in the gaseous state

1

(iv) recycled

allow reused or returned to the reactor

1

(b) reversible arrows

1

hydrogen and ammonia

1

[9]

Q14.

(a) (i) natural gas

allow fossil fuels / biogas generator

1

(ii) air contains oxygen

1

this would react with / oxidise the hydrogen

allow this would react with / oxidise the iron

ignore nitrogen

1

(iii) cooled

1

ammonia condenses / liquefies (so can be separated)

1

nitrogen and hydrogen (remain as gases and) are returned to the reactor

allow recycled

1

(b) (i) 200 °C and 1000 atmospheres

1

(ii) the reaction is reversible

allow stated as equilibrium or forward / backward reaction anywhere in answer

1

forward reaction is exothermic so increased temperature lowers the yield of ammonia

allow converse

1

a lower temperature would decrease rate of reaction

allow converse

1

a higher pressure would increase the yield of ammonia because the forward reaction produces the least number of (gaseous) molecules / moles

allow converse

1

higher pressures would involve high cost / energy

1

ignore risk / explosion

[12]

Q15.

(a) (i) Filtration

1

(ii) Chlorine

1

(b) (i) nanoparticles are small / smaller / much smaller / tiny

allow any in range 1−100 nm or 1 × 10-9 m − 1 × 10-7 m or a few hundred atoms in size

ignore numbers if stated smaller

1

(ii) they have a high surface area to volume ratio

reference to surface area without volume ratio is insufficient

allow nanoparticles are very reactive or nanoparticles are more reactive than normal particles.

1

(c) (sodium hydroxide) produces a white precipitate

accept solid / suspension or ppt or ppte for precipitate.

ignore cloudy / milky

1

which (then) dissolves / disappears (in excess sodium hydroxide)

M2 cannot be awarded unless a solid of some sort has been made

ignore names or formulae of compounds

1

[6]

Q16.

(a) because sulfur dioxide causes acid rain

1

which kills fish / aquatic life or dissolves / damages statues / stonework or kills / stunts growth of trees

if no other mark awarded then award 1 mark for sulfur dioxide is toxic or causes breathing difficulties.

1

(b) (i) electrons are lost

1

(ii) Cu2+ + 2e−→ Cu

allow Cu2+→ Cu − 2e−

ignore state symbols

1

(iii) copper sulfate

allow any ionic copper compound

1

(c) (lattice of) positive ions

1

delocalised electrons

accept sea of electrons

1

(electrostatic) attraction between the positive ions and the electrons

1

electrons can move through the metal / structure or can flow

allow electrons can carry charge through the metal / structure

if wrong bonding named or described or attraction between oppositely charged ions then do not award M1 or M3 − MAX 2

1

(d) (copper compounds are absorbed / taken up by) plants

allow crops

1

which are burned

1

the ash contains the copper compounds

do not award M3 if the ash contains copper (metal)

1

(e) / Ar 55.6 / 63.5 16.4 / 56 28.0 / 32

moles 0.876 0.293 0.875

ratio 3 1 3

formulaCu3FeS3

award 4 marks for Cu3FeS3 with some correct working

award 3 marks for Cu3FeS3 with no working

if the answer is not Cu3FeS3 award up to 3 marks for correct steps from the table apply ecf

if the student has inverted the fractions award 3 marks for an answer of CuFe3S

4

[16]

Q17.

(a) gold

1

(b) atom (s)

1

(c) (i) protons

any order

allow proton

1

neutrons

allow neutron

1

(ii) 3 / three

1

(d) (i) Al

ignore any numbers / charges

1

(ii) any two from:

• limited resource

• expensive in terms of energy / mining

• effects on the environment, such as, landfill, atmospheric pollution, quarrying

allow uses a lot of energy to extract.

2

(e) resistant to corrosion

1

does not react (with water or food)

allow one mark for low density with a suitable reason given

1

[10]

Q18.

(a) (i) central block

1

(ii) conducts electricity

1

(b) any two from:

• visual pollution

• noise pollution

• dust pollution

• habitat destruction.

2

(c) (i) to concentrate the ore / copper carbonate

or

to remove / separate the rock

1

(ii) 12 (tonnes)

If answer is incorrect allow one mark for (127 + 132) − 247 or

259 - 247

2

(iii) any one from:

• so no reactant is wasted / left unreacted

• so they know how much product they will make

• need to record / compensate for the carbon dioxide produced

allow so they can work out their carbon footprint.

1

[8]

Q19.

(a) The ore is not pure or contains impurities or the ore does not contain 100% of the metal compound

allow to concentrate the metal or metal compound

1

rock / other compounds need to be removed / separated

1

(b) (i) (cast iron is) brittle

allow not strong

ignore weak

1

(ii) the oxygen reacts with carbon

allow carbon burns in oxygen or is oxidised

1

reducing the percentage of carbon in the mixture

or producing carbon dioxide

1

(c) (i) aluminium has a low density

1

(ii) (because copper) is in the central / middle (block of the periodic table)

1

whereas aluminium is in Group 3 (of the periodic table)

1

(iii) iron is more reactive (than copper)

ignore cost

1

so copper is displaced / reduced

1

[10]

Q20.

(a) sodium loses (electron)

sharing / covalent / metallic = max 2

1

chlorine gains (electron)

1

1 or an (electron)

1

(b) (i) Have no overall electric charge

1

(ii) Should iodine be added to salt?

1

reason

any one from:

• cannot be done by experiment

accept difficult to get / not enough evidence

• based on opinion / view

allow must be done by survey

• ethical or economic issue.

1

(c) (i) nitric (acid)

1

(ii) an alkali

1

(iii) indicator

accept any named acid base indicator

1

(d) (i) Crystallisation

1

(ii) fertiliser

allow to help crops grow

1

(iii) any one from:

• pressure

allow concentration

• temperature

ignore heat

• catalyst.

1

[12]

Q21.

(a) giant structure / lattice / layers / close packed

first 3 marks can be obtained from a suitably labelled diagram

incorrect structure or bonding or particle = max 3

1

made up of atoms / positive ions

1

with delocalized / free electrons

1

so electrons can move / flow through the metal

accept so electrons can carry charge through the metal

accept so electrons can form a current

1

(b) an alloy (is a metal which) has different types / sizes of atoms

accept converse for pure metal throughout

both marks can be obtained from suitable diagrams

allow made of different metals

allow mixture of metals / atoms / elements

ignore particles

ignore properties

do not accept compound

1

alloy has distorted layers

allow layers are unable to slide

1

(c) (i) can return to its original shape

accept shape memory alloy

accept smart alloy

ignore other properties

1

(ii) (pure copper is too) soft

accept converse

accept malleable or bends

accept copper is running out

ignore references to strength and weakness

1

(iii) aluminium oxide

accept alumina

accept Al2O3

ignore bauxite / aluminium ore

1

(iv) any one from:

• different conditions

• different catalyst

• different pressure

allow different concentration

• different temperature.

do not accept different monomers

1

(d) any two from:

• accurate

• sensitive

• rapid

• small sample.

both needed for 1 mark

1

[11]

Q22.

(a) (i) Solids

1

(ii) Chlorine

1

(iii) kill microbes / bacteria

allow to make the water safe to drink

ignore disinfect

ignore remove / get rid of microbes

1

(b) energy

allow heat

1

(c) improve dental health

allow reduce tooth decay

allow (local) government requirement

allow help teeth

1

[5]

Q23.

(a) natural gas

allow correct answer shown in box if answer line blank

1

(b) (i) 450

allow correct answer shown in box if answer line blank

1

(ii) iron

allow correct answer shown in box if answer line blank

1

(iii) The catalyst lowers the activation energy.

1

(c) (the gases are) cooled

1

ammonia condenses

allow ammonia liquefies

1

nitrogen and hydrogen are recycled

if no other mark awarded allow ammonia is separated for 1 mark

1

[7]

Q24.

(a) (i) nothing can enter and nothing can leave the reaction

allow sealed reaction vessel

1

(ii) forward and backward reactions have same rate

1

so there is no (overall) change in quantities of reactants and products

allow concentrations of reactants and products

1

(b) (i) natural gas

allow methane / CH4

allow fossil fuels / hydrocarbons

allow water

1

(ii) provides an alternative reaction pathway

1

which has a lower activation energy

ignore references to collisions

1

(iii) the amount (of ammonia) increases

allow yield increases

1

the equilibrium moves to the side (of the equation) with fewer (gaseous) molecules / moles

allow it favours the forward reaction

1

(c) (i) vertical arrow from reactants to maximum

1

(ii) (energy of) products higher than (energy of) reactants

allow converse

1

(iii) amount of hydrogen iodide decreases

1

equilibrium moves in the direction of the endothermic reaction

allow it favours the forward reaction

1

[12]

Q25.

(a) (i) Solids

1

(ii) Chlorine

1

(iii) improves dental health or reduces tooth decay

1

(b) put a sample of the filtered water in an evaporating basin or leave to evaporate

accept any description of evaporation (using a Bunsen or leaving on the windowsill)

1

there will be crystals of salt left

1

(c) sodium and / or chloride ions are bigger than water (molecules) or ions are charged or molecules are not charged

do not accept sodium chloride molecules as ions is given in the question

1

[6]

Q26.

(a) (i) brown

1

(ii) oxygen + iron + water hydrated iron oxide / rust

allow correct symbol equation

ignore oxidation numbers for product

1

(b) (i) 32.3

1

(ii) 7.6

ecf from (b)(i)

1

(iii) do not know start volume of air

1

because the burette not graduated to the end

allow iron wool takes up some of the space

if no other marks awarded accept all iron may have rusted (1) or still some oxygen left / not all used up (1)

1

(c) (i) gains oxygen and water or oxygen and water are added

allow reacts with or gains oxygen

allow reacts with or gains water

allow reacts with or gains elements which add to mass

ignore iron oxide forms

1

(ii) as temperature increases (from 10 °C to 42 °C or to 50 °C) the increase in mass of nail increases

accept positive correlation

accept mass increases

1

rate of increase gets faster as temperature goes up

accept exponential

ignore non linear

1

no further increase at temperatures over 42 °C

accept no further increase at high temperatures

exponential increase scores 2 marks

1

(iii) use a (bigger) flask or let air into the tube or leave for less time or

ignore more water

1

to make sure sufficient oxygen / air or not all oxygen used up

accept converse

if no other marks awarded allow change in surface area for rusting or change in number of nails for 1 mark

1

[12]

Q27.

(a) pure copper is twice as good a conductor as 99% pure copper

accept reverse argument

accept answers quoting 2 correct values from the graph scores 2

qualitative answer (e.g. pure copper is a better conductor than impure copper) scores 1

or

answers quoting a conductivity value from the graph scores 1

2

(b) Marks awarded for this answer will be determined by the Quality of Communication (QC) as well as the standard of the scientific response.

0 marks

No relevant content

Level 1 (1–2 marks)

Simple list of a limited number of points given, with no linking between ideas

Level 2 (3–4 marks)

A broader set of points made. There will probably not be links between ideas

Level 3 (5–6 marks)

Answer includes linking between ideas, showing the consequence of either not recycling or the advantage of recycling. Answers such as less fossil fuel needed so less carbon dioxide produced or less carbon dioxide produced so less global warming

examples of the points made in the response

resources

(recycling) conserves supplies of ores

copper available for longer

as (at present rate of use) copper ores will run out in about 35 years

(recycling) conserves supplies of fossil fuels or energy

less fuel used at a lower cost

land pollution

mining scars landscape or produces noise pollution

mining destroys wildlife habitats

(recycling) less need to mine ores / fossil fuels

so less habitat destroyed or less scarring of landscape

(recycling) less need to use landfill for waste

atmospheric pollution

burning fossil fuels produces carbon dioxide / greenhouse gas

which (may) cause global warming or climate change

extraction produces sulfur dioxide

which causes acid rain

which can kill trees / fish

6

(c) grow plants

accept plants absorb copper (through roots)

1

then plants are burned

1

ash (from burning) contains copper compounds

1

[11]

Q28.

(a) (i) economical

1

(ii) phytomining

1

(iii) carbon dioxide

1

(b) (i) copper / Cu

1

iron sulfate / FeSO4

1

(ii) copper / ions have a positive charge

it = copper ions

allow copper ions have a different charge

accept copper / ions are free to move

accept to gain electrons

accept copper / ions are attracted to the negative electrode or opposite charges attract

1

(c) any two from:

ignore not biodegradable or does not decay

• copper ores are limited / running out

allow copper is running out

• copper can be recycled

• copper can be reused

• copper is expensive

• landfill sites are filling up

• copper compounds are toxic

allow copper is toxic

2

[8]

Q29.

(a) (i) phytomining

1

(ii) (the land contains) very little copper

allow low grade ore or large amounts of waste

ignore quarrying / benefits of using plants

1

uneconomical

accept (smelting) uses a lot of energy / fossil fuels

allow expensive

1

(iii) Cu

1

2 CuO + C ➔ 2 Cu + CO2

allow 2 CuO + C ➔ Cu2 + CO2 for 1 mark

1

(b) (i) iron is more reactive (than copper)

1

iron is cheap(er than copper)

allow cheaper or uses less energy than electrolysis

1

(ii) any two from:

• copper / ions move or are attracted to the negative electrode / cathode

• where they are reduced or gain (two) electrons

• where they form copper (metal / atoms)

2

[9]

Q30.

(a) alloy

1

(b) in mixture:

different sized / bigger atoms

1

so there are no layers / rows / lines (to slide)

accept converse

1

(c) any two from:

ignore references to bend and mould

• cost

• toxicity

• strength

• appearance of brace

• unreactive or resistant to corrosion / saliva

allow rusting as alternative to corrosion

2

(d) crosslinks

allow lines / bonds between the rows / chains

1

[6]

Q31.

(a) filter

1

to remove solids or insoluble particles

OR

add coagulant (1)

flocculation / settling / remove solids (1)

1

(add) chlorine

accept ozone / UV

1

to reduce the number of microbes

accept to kill microbes / bacteria / germs

accept sterilise

allow disinfect

ignore remove microbes

1

(b) (i) ion exchange resin

allow ion exchange column

allow sodium ions / Na+

allow hydrogen ions / H+

1

(ii) prevent growth of microbes

accept sterilise

accept to kill microbes / bacteria / germs

accept to reduce the number of microbes

ignore remove microbes

1

(c) high cost of energy / heating

allow uses a lot of energy

1

(d) any one from:

• helps to develop / maintain bones

allow any suitable positive effect on bones

• helps to develop / maintain teeth

allow any suitable positive effect on teeth

• reduces heart disease

1

[8]

Q32.

(a) 2NH3

allow NH3 with incorrect or missing balancing for 1 mark

allow multiples

2

(b) (i) 200

1

(ii) rate of reaction (too) slow

allow converse

ignore references to yield / cost

1

(iii) 400

1

(iv) lower yield

allow converse

accept shifts equilibrium to left

allow favours the backward reaction

allow favours side with more (gaseous) molecules

allow lower rate

1

(c) (gases) cooled

it = ammonia

1

ammonia liquefied

accept ammonia condensed

accept ammonia cooled below boiling point for 2 marks

1

[8]

Q33.

(a) (i) an alloy

1

(ii) harder

1

(b) (i) 162.5

correct answer with or without working gains 2 marks

if no answer or incorrect answer then evidence of correct working [56 + (3x35.5)] gains 1 mark

2

(ii) 34.46

accept rounding from 34 - 34.5

correct answer with or without working gains 2 marks

accept ecf from (b)(i) correctly calculated for 2 marks

if no answer or incorrect answer then evidence of 56 / 162.5 or 56 / answer to (b)(i) gains

1 mark

2

[6]

Q34.

(a) (Chromium =) 20

in correct order

1

(Nickel =) 8

accept Chromium = 8 and Nickel = 20 for 1 mark

1

(b) (i) (because iron is made up of only) one type of atom

1

(ii) not strong

allow too soft or too flexible

accept it rusts / corrodes or that it could wear away

accept could change shape / bend

accept layers / atoms could slide (over each other)

1

(iii) structure is different / distorted / disrupted

accept not in layers or not regular

1

so it is difficult for layers / atoms / particles to slip / slide (over each other)

accept layers cannot slip / slide

1

[6]